One big advantage of the system over FDD (Frequency Division Duplex) system is channel reciprocity. The channel reciprocity is based on the assumption that a property of downlink channel is the same as that of uplink channel in same frequency bandwidth. For example, if a reception side sends sounding signals through sounding channel (it composes uplink channel), a transmission side can obtain information about downlink channel by estimating the uplink channel by using sounding signals.
If we can exploit the reciprocity of channel sufficiently, we can greatly reduce required CINR, which is very important for most mobile communication systems.
There are two deciding factor of the channel reciprocity: velocity and TX-RX link symmetry. If a velocity of user is high (fast fading channel), we can not utilize the channel reciprocity effectively. However, if the velocity of user is low, we can obtain the channel reciprocity by maintaining appropriate TX-RX link configuration.